Citizen of the Galaxy (1957) by Robert A Heinlein

Wikipedia wrote:Citizen of the Galaxy is a science fiction novel by American writer Robert A. Heinlein, originally serialized in Astounding Science Fiction (September, October, November, December 1957) and published in hardcover in 1957 as one of the Heinlein juveniles by Scribner's. The story is heavily influenced by Rudyard Kipling's Kim.

Wikipedia wrote:Thorby is a young, defiant slave boy recently arrived on the planet Jubbul's capital Jubbulpore, where he is purchased by an old beggar, Baslim the Cripple, for a trivial sum and taken to the beggar's surprisingly well-furnished underground home. Thereafter Baslim treats the boy as a son, teaching him not only the trade of begging, but also mathematics, history, and several languages, and sends Thorby on errands all over the city, carefully passing along information and keeping track of the comings and goings of starships, so that Thorby realizes that his foster-father is gathering intelligence, particularly on the slave trade. In addition, Baslim has Thorby memorize a contingency plan and a message to deliver to one of five starship captains in the event of Baslim's arrest or death. When Baslim is captured and beheaded by the local authorities, Thorby and local innkeeper 'Mother Shaum' convey the message to Captain Krausa of the starship Sisu. Because the 'Free Trader' society to whom Krausa belongs owes a debt to Baslim for the rescue of one of their crews from a slave trader, the captain takes Thorby aboard the Sisu at great risk to himself and his clan.

Thorby is adopted by the captain (thereby gaining considerable shipboard social status) and adjusts to the insular, clannish, matriarchal culture of the traders. The advanced education provided by Baslim and the fast reflexes of youth make him an ideal fire controlman, in which position Thorby destroys a pirate craft. His immediate superior, a young woman named Mata, begins to view him as a suitable husband—but the customs of the Free Traders forbid this, and to avoid trouble she is transferred to another ship.

Thorby is again transferred when the captain, against the wishes of his wife, the executive officer and head of the clan (who wants to use Thorby's connection to Baslim to enhance Sisu's prestige), obeys Baslim's last wish, entrusting the boy to a military cruiser and asking its captain to assist Thorby in finding his true place in society. In order to implement a background search without having to pay the immense cost, Thorby is enlisted in the military service of the Terran Hegemony, the dominant military power in the galaxy.